An Infernal urn can be created at 62 Crafting (assist system can be used) with two pieces of soft clay and an air rune. Making it from the potter's wheel gives 40 Crafting experience, and firing it gives it 60, making it a total of 100 per urn. It is used with Prayer to help with gaining experience.
The urn fills with experience the player would have earned if the ashes had been scattered instead of collected. The urn is filled when the player would have earned 1,562.5 Prayer experience with the urn in inventory.

Once the infernal urn is full, it can be teleported to Ernie for 1,875 Prayer experience, which is a 20% Prayer experience bonus for all types of demonic ashes, compared to the base experience given for scattering them.

The Infernal urn essentially acts as a temporary Bonecrusher for demon-type ashes. Once ashes have been collected into the urn, they cannot be removed. Scattering ashes already in a player's inventory does not fill the urn. The urn cannot be used with altars or the Ectofuntus.

Having an infernal urn may not be the most efficient way to train prayer; however, it may be one of the fastest with the inventory spaces saved. Using the Ectofuntus yields more experience per ashes, but takes more time - banking and gathering slime - the slime requirement can be reduced using the Morytania Tasks buckets from Robin. If a player uses 25 infernal ashes with an infernal urn, this would result in 1,875 prayer experience. If the ashes were instead used on the ectofuntus, this would instead result in 6,250 prayer experience.

If you started this urn, and die with it, it will be destroyed and will not appear at your gravestone.

The blue stripes on the urn seem to get darker on HD when it fills up (a tint for every quarter).

If you have 10 Infernal Urn (full) you will no longer be able to collect ashes in urns. You will be prompted with a message saying: "You should get rid of some of your prayer urns before starting a new one."

When checked on 50%, it says "This infernal urn is half full, or is it half empty?" in reference to how optimists and pessimists perceive things differently.